GHSA-f8h2-vmm9-qhj6 BIT-aspnet-core-2026-45591 BIT-dotnet-2026-45591 BIT-dotnet-sdk-2026-45591 CVE-2026-45591
Microsoft Security Advisory CVE-2026-45591 – ASP.NET Core Denial of Service Vulnerability
High
NuGet
- Severity
- 7.5 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 2.48%
- Chance of exploitation in the next 30 days. Higher than 84.58% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
- Available
- 4 packages have a fixed version
Description
Executive summary
Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core SignalR and Blazor Server. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.
A denial of service vulnerability exists in the MessagePack hub protocol used by SignalR and Blazor Server where an attacker can send deeply-nested MessagePack arrays to cause a stack overflow, resulting in a denial of service.
Announcement
Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/405
Affected Platforms
- Platforms: All
- Architectures: All
<a name="affected-packages"></a>Affected Packages
The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below
<a name=".NET 10"></a>.NET 10
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.AspNetCore.App.Runtime.linux-arm | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.linux-arm64 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-arm | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-x64 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.osx-x64 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.win-arm | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.win-arm64 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.win-x64 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
| Microsoft.AspNetCore.App.Runtime.win-x86 | >= 10.0.0, <= 10.0.8 | 10.0.9 |
<a name=".NET 10 SignalR"></a>Microsoft.AspNetCore.SignalR.Protocols.MessagePack (.NET 10)
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack | >= 10.0.0, <= 10.0.8 | 10.0.9 |
<a name=".NET 9"></a>.NET 9
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.AspNetCore.App.Runtime.linux-arm | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.linux-arm64 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-arm | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-x64 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.osx-x64 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.win-arm | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.win-arm64 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.win-x64 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
| Microsoft.AspNetCore.App.Runtime.win-x86 | >= 9.0.0, <= 9.0.16 | 9.0.17 |
<a name=".NET 9 SignalR"></a>Microsoft.AspNetCore.SignalR.Protocols.MessagePack (.NET 9)
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack | >= 9.0.0, <= 9.0.16 | 9.0.17 |
<a name=".NET 8"></a>.NET 8
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.AspNetCore.App.Runtime.linux-arm | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.linux-arm64 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-arm | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.linux-musl-x64 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.osx-x64 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.win-arm | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.win-arm64 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.win-x64 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
| Microsoft.AspNetCore.App.Runtime.win-x86 | >= 8.0.0, <= 8.0.27 | 8.0.28 |
<a name=".NET 8 SignalR"></a>Microsoft.AspNetCore.SignalR.Protocols.MessagePack (.NET 8)
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack | >= 8.0.0, <= 8.0.27 | 8.0.28 |
Advisory FAQ
<a name="how-affected"></a>How do I know if I am affected?
If using a package listed in affected packages, you're exposed to the vulnerability.
<a name="how-fix"></a>How do I fix the issue?
- To fix the issue please install the latest version of .NET 10.0, .NET 9.0, or .NET 8.0. If you have installed one or more .NET SDKs through Visual Studio, Visual Studio will prompt you to update Visual Studio, which will also update your .NET SDKs.
- If your application references the vulnerable package, update the package reference to the patched version. You can list the versions you have installed by running the
dotnet --infocommand.
- If you're using .NET 8.0, you should download and install .NET 8.0.28 Runtime or .NET 8.0.xxx SDK from https://dotnet.microsoft.com/download/dotnet-core/8.0.
- If you're using .NET 9.0, you should download and install .NET 9.0.17 Runtime or .NET 9.0.xxx SDK from https://dotnet.microsoft.com/download/dotnet-core/9.0.
- If you're using .NET 10.0, you should download and install .NET 10.0.9 Runtime or .NET 10.0.xxx SDK from https://dotnet.microsoft.com/download/dotnet-core/10.0.
Once you have installed the updated runtime or SDK, restart your apps for the update to take effect.
Additionally, if you've deployed self-contained applications targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed.
Other Information
Reporting Security Issues
If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.
Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.
Support
You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repos are located at https://github.com/dotnet/aspnetcore. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue.
Disclaimer
The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
Acknowledgements
Anonymous
Affected versions
NuGet
| Package | Vulnerable | Fixed in |
|---|---|---|
| Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 8.0.0, < 8.0.28 |
8.0.28 |
| Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 9.0.0, < 9.0.17 |
9.0.17 |
| Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 10.0.0, < 10.0.9 |
10.0.9 |
| Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 8.0.0, < 8.0.28 |
8.0.28 |
| Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 9.0.0, < 9.0.17 |
9.0.17 |
| Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 10.0.0, < 10.0.9 |
10.0.9 |
| Microsoft.AspNetCore.App.Runtime.win-x64 | >= 8.0.0, < 8.0.28 |
8.0.28 |
| Microsoft.AspNetCore.App.Runtime.win-x64 | >= 9.0.0, < 9.0.17 |
9.0.17 |
| Microsoft.AspNetCore.App.Runtime.win-x64 | >= 10.0.0, < 10.0.9 |
10.0.9 |
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack | >= 8.0.0, < 8.0.28 |
8.0.28 |
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack | >= 9.0.0, < 9.0.17 |
9.0.17 |
| Microsoft.AspNetCore.SignalR.Protocols.MessagePack | >= 10.0.0, < 10.0.9 |
10.0.9 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
Microsoft.AspNetCore.App.Runtime.linux-x64 NuGet → 8.0.28
- dotnet
dotnet add package Microsoft.AspNetCore.App.Runtime.linux-x64 --version 8.0.28
Microsoft.AspNetCore.App.Runtime.osx-arm64 NuGet → 8.0.28
- dotnet
dotnet add package Microsoft.AspNetCore.App.Runtime.osx-arm64 --version 8.0.28
Microsoft.AspNetCore.App.Runtime.win-x64 NuGet → 8.0.28
- dotnet
dotnet add package Microsoft.AspNetCore.App.Runtime.win-x64 --version 8.0.28
Microsoft.AspNetCore.SignalR.Protocols.MessagePack NuGet → 8.0.28
- dotnet
dotnet add package Microsoft.AspNetCore.SignalR.Protocols.MessagePack --version 8.0.28
Severity breakdown
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Weakness
CWE-400: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How to prevent it
- Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
- Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
- Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
- Implementation: Ensure that all failures in resource allocation place the system into a safe posture.
CWE-787: Out-of-bounds Write
The product writes data past the end, or before the beginning, of the intended buffer.
How to prevent it
- Requirements: Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.
- Operation, Build and Compilation: Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
- Implementation: Consider adhering to the following rules when allocating and managing an application's memory: Double check that the buffer is as large as specified. When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string. Check buffer boundaries if accessing the buffer in a loop and make sure there is no danger of writing past the allocated space. If necessary, truncate all input strings to a reasonable length before passing them to the copy and concatenation functions.
- Operation, Build and Compilation: Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code. Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking. For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
- Operation: Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment. For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].
- Implementation: Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.
References
Advisories
Packages
Other links
- github.com/dotnet/aspnetcore/security/advisories/GHSA-f8h2-vmm9-qhj6
- github.com/dotnet/announcements/issues/405
- github.com/dotnet/aspnetcore/discussions/67100
- msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45591
- access.redhat.com/errata/RHSA-2026:17527
- access.redhat.com/errata/RHSA-2026:25110
- access.redhat.com/errata/RHSA-2026:25111
- access.redhat.com/errata/RHSA-2026:25112
- access.redhat.com/errata/RHSA-2026:25113
- access.redhat.com/errata/RHSA-2026:25114
- access.redhat.com/errata/RHSA-2026:25115
- access.redhat.com/errata/RHSA-2026:25220
- access.redhat.com/errata/RHSA-2026:25221
- access.redhat.com/errata/RHSA-2026:25222
- access.redhat.com/errata/RHSA-2026:26638
- access.redhat.com/errata/RHSA-2026:26994
- access.redhat.com/errata/RHSA-2026:28007
- access.redhat.com/errata/RHSA-2026:28009
- access.redhat.com/errata/RHSA-2026:28011
- access.redhat.com/errata/RHSA-2026:28051
- access.redhat.com/errata/RHSA-2026:28227
- access.redhat.com/security/cve/CVE-2026-45591
- bugzilla.redhat.com/show_bug.cgi
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-45591.json
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-vmch-3w2x-vhgq .NET Denial of Service Vulnerability | High Known exploited | Also affects Microsoft.AspNetCore.App.Runtime.win-x64 |
| GHSA-f4g7-52wc-p8x7 Microsoft Security Advisory CVE-2026-96236 - ASP.NET Core Denial of Service Vulnerability | High | Also affects Microsoft.AspNetCore.App.Runtime.linux-x64 |
| GHSA-rv87-ccxw-8ggf Microsoft Security Advisory CVE-2026-88092 - ASP.NET Core Security Feature Bypass Vulnerability | Critical | Also affects Microsoft.AspNetCore.App.Runtime.linux-x64 |
| GHSA-57xr-hfxx-jw5x Microsoft Security Advisory CVE-2026-70196 - ASP.NET Core Denial of Service Vulnerability | Medium | Also affects Microsoft.AspNetCore.App.Runtime.linux-x64 |
| GHSA-fpq8-4vhr-rcxx Microsoft Security Advisory CVE-2026-70188 - ASP.NET Core Security Feature Bypass Vulnerability | Critical | Also affects Microsoft.AspNetCore.App.Runtime.linux-x64 |
| GHSA-mf4x-w4gh-4656 Microsoft Security Advisory CVE-2026-70186 - ASP.NET Core Denial of Service Vulnerability | High | Also affects Microsoft.AspNetCore.App.Runtime.linux-x64 |
| GHSA-494h-xx7x-5frh Microsoft Security Advisory CVE-2026-70183 - ASP.NET Core Security Feature Bypass Vulnerability | High | Also affects Microsoft.AspNetCore.App.Runtime.linux-x64 |
| GHSA-w5qq-qrpp-rf4c Microsoft Security Advisory CVE-2026-70181 - ASP.NET Core Denial of Service Vulnerability | High | Also affects Microsoft.AspNetCore.App.Runtime.linux-x64 |
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